JPH1079139A - optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve resistance against heat and vibration in an optical disc in which resin substrates are stuck together with a larger ratio of the diameter to the thickness thereof. SOLUTION: A pair of resin substrates is arranged and at least one of the resin substrates is provided with an information carrying part. The pair of resin substrates are bonded by an adhesive so as to seal in the information carrying part and when the thickness of the resin substrate is represented by t and the diameter ϕ thereof, ϕ/t of each resin substrate exceeds 180. The Young modulus of the bonded layer at 20 deg.C is 0.1kgf/mm<2> or more to 1kgf/mm<2> or less while the kinematic loss coefficient tan δ at 20 deg.C thereof is 0.6-5.0. The bonded layer is composed of a hot melt type adhesive, a pressure sensitive agent, a normally hardening type adhesive, an ultraviolet hardening type adhesive or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical disk, for example, a rewritable optical recording disk such as a phase-change optical recording disk, a write-once optical recording disk, and a read-only optical disk.

[0002]

2. Description of the Related Art Commercially available laser disks (L
D) and a 5.25-inch magneto-optical disk have a thickness of 1.2 mm.
An information carrying portion is provided on the surface of the resin substrate, and the information carrying portion is bonded with an adhesive layer so as to be enclosed. A hot-melt adhesive is mainly used for the adhesive layer (Japanese Patent Application Laid-Open No. 58-6536). Also,
The compact disk (CD) has a single-plate configuration in which a reflective film and a resin protective film are merely provided on an information carrying portion of a resin substrate having a thickness of 1.2 mm.

Recently, however, a resin substrate having a thickness of 0.6 mm is being put to practical use because of the necessity of narrowing down a laser beam in order to increase the information carrying density of an optical disk. As a result, the mechanical strength of the resin substrate is reduced to 1/4, so that the resin substrate cannot be used as a single plate like a CD. For this reason, it has been proposed to adopt a configuration in which two resin substrates are bonded together as employed in LDs and the like.

[0004] An optical disk having a resin substrate having a thickness of 0.6 mm bonded thereto has an extremely high information carrying density, and has a small diameter equivalent to that of a CD, but has a large capacity, and is about to be used as a digital video disk. And, because of its small diameter, use in automobiles is also considered.

However, considering use in a car,
It is necessary to take measures against in-vehicle environment such as high temperature and vibration. For example, when exposed to direct sunlight, the interior of the vehicle may reach a temperature of 80 ° C. or higher, so that the adhesive used for bonding the substrates is required to have high heat resistance. Conventional hot-melt adhesives generally used in the optical disc field are softened in a high-temperature environment and their adhesive strength is reduced, so that there is a problem that the mechanical strength of the optical disc is deteriorated.

As an adhesive having high heat resistance, for example, a reaction-curable adhesive as described in JP-A-61-110350 can be mentioned. Once cured, reaction-curable adhesives do not soften like hot-melt adhesives, even when the ambient temperature rises.
Good heat resistance. As the reaction-curable adhesive, an ultraviolet-curable adhesive is mainly used because it cures in a short time.

However, it has been found that an optical disk using an adhesive having good heat resistance has poor stability against vibration. Adhesives with good heat resistance have a high Young's modulus near room temperature. Therefore, when vibration is applied to a rotating optical disk, the adhesive layer cannot absorb the vibration, and the surface of the optical disk is Shake occurs, which causes a problem at the time of recording and reproduction, particularly at the time of recording. In particular, when a substrate having a large ratio of the diameter to the thickness is used, the substrate is easily affected by vibration.

It has been found that even a hot melt adhesive having a high melting point has good heat resistance, but also in this case, the stability against vibration is also deteriorated.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to improve both heat resistance and vibration resistance of an optical disk having a structure in which resin substrates having a large ratio of diameter to thickness are bonded.

[0010]

This and other objects are achieved by any one of the following constitutions (1) to (5). (1) A pair of resin substrates are provided, and at least one of the resin substrates is provided with an information carrying portion, and the pair of resin substrates is bonded by an adhesive layer so that the information carrying portion is enclosed. When the thickness of the resin substrate is t and the diameter thereof is φ, φ / t of each resin substrate is 180 or more, and the Young's modulus of the adhesive layer at 20 ° C. exceeds 0.1 kgf / mm ^2.
An optical disk having a kgf / mm ² or less and a mechanical loss coefficient tan δ at 20 ° C. of 0.6 to 5.0. (2) The optical disc according to (1), wherein the adhesive layer is made of a hot melt type adhesive. (3) The optical disc according to (1), wherein the adhesive layer is made of an adhesive. (4) The optical disc according to (1), wherein the adhesive layer is formed of a room temperature-curable adhesive. (5) The optical disc according to (1), wherein the adhesive layer is made of an ultraviolet curable adhesive.

[0011]

[Action and Effect] As described above, the adhesive having high heat resistance has a high Young's modulus near room temperature. On the other hand, in a vibration environment assuming the interior of an automobile, the stability was examined by rotating an optical disc with a resin substrate bonded with various adhesives. It was found that an adhesive having a low but low Young's modulus near room temperature absorbs vibration and thus contributes to improvement of rotational stability. Also, it was found that when the mechanical loss coefficient tanδ near normal temperature was small, the vibration absorption was insufficient, whereas when the tanδ was large, the heat resistance was insufficient.

Therefore, in the present invention, by limiting the physical properties of the adhesive as described above, both the heat resistance and the vibration resistance can be satisfied, and the above object has been achieved.

JP-A-2-292745, 2-2
Japanese Patent No. 92746 specifies physical properties of a hot-melt adhesive. However, these hot-melt adhesives are out of the range of the present invention in physical properties and insufficient in heat resistance.

In the present invention, the information carrying unit is C
D refers to both a surface that previously holds information, such as a pit formation surface of a read-only optical disk such as D, and a recording film of an optical recording disk.

[0015]

Embodiments of the present invention will be described below in detail.

[0016] <Adhesive layer> adhesive layer, the Young's modulus at 20 ° C. is 0.1 kgf / mm ² Ultra 1 kgf / mm ² or less, preferably 0.12~1kgf / mm ^2, mechanical loss factor at 20 ° C. tan δ is 0.6 to 5.0, preferably 1.5 to
3.0. If the Young's modulus is too low or tan δ is too large, the heat resistance becomes insufficient, and the optical disk is likely to warp when used in a high-temperature environment. Specifically, since the adhesive layer becomes too soft in a high-temperature environment, a shift occurs between the resin substrates when the optical disk bends under its own weight. When the temperature returns to room temperature, the adhesive strength also returns, so that the deflection is fixed. On the other hand, if the Young's modulus is too high or tan δ is too small, vibration absorption will be insufficient.

The Young's modulus and the mechanical loss coefficient tan δ are measured as follows. The adhesive is applied on a release paper, for example, using a roll coater or the like so as to have a thickness of 100 to 500 μm. Those that need to be cured are cured under the same conditions as when the optical disk is manufactured. After curing, the adhesive is peeled from the release paper to obtain an adhesive layer sample. This sample is measured at a vibration frequency of 10 Hz (sine wave) by a forced vibration method using a viscoelasticity measuring device.

The adhesive constituting the adhesive layer is not particularly limited, and may be, for example, any of a hot-melt adhesive, an ultraviolet-curable adhesive, a room-temperature-curable adhesive, and the like. Good.

The base polymer of the hot melt adhesive is not particularly limited as long as it has tackiness at room temperature, but it is preferable to use a thermoplastic block copolymer elastomer. As a block component of the thermoplastic block copolymer elastomer, polystyrene, polybutadiene, polyisoprene, ethylene-butylene copolymer, and the like are preferable, and it is preferable to use one or more of these. In particular, a block copolymer elastomer of polystyrene having a molecular weight of about 2000 to 12500 and polybutadiene, polyisoprene or an ethylene-butylene copolymer having a molecular weight of about 1000 to 250,000 is preferable. The molecular weight of the block copolymer elastomer is 3
It is preferably about 000 to 500,000. Base polymers include, in addition to these thermoplastic block copolymer elastomers, synthetic rubbers such as isoprene rubber, styrene rubber, butadiene rubber, and butyl rubber; polyolefins such as polyethylene, polypropylene, and ethylene-vinyl acetate copolymer; and polyolefin-based copolymers. It is preferable that one or more kinds such as coalescence are contained as necessary.

The hot-melt adhesive containing an ultraviolet-curable component, which will be described later, can be used as a hot-melt adhesive, and can also be polymerized by irradiation with ultraviolet rays, electron beams, or the like.

The UV-curable adhesive contains at least a UV-curable component and a photopolymerization initiator. As the ultraviolet curable component, an oligomer of a saturated hydrocarbon resin having at least one acryloyl group having a double bond exhibiting sensitivity to an ultraviolet ray or an electron beam in one molecule is preferable. Examples of such oligomers include acrylates, urethane acrylates of saturated hydrocarbon resin oligomers containing at least one hydroxyl group or carboxyl group in one molecule such as hydrogenated polybutadiene, polybutene, hydrogenated polyisoprene, and polyisobutylene. Epoxy acrylate or ester acrylate is preferable, and it is preferable to use one or more of these. In order to reduce the Young's modulus of the adhesive layer after curing at room temperature, for example, an acrylate monomer or acrylate oligomer having a long-chain molecule such as a long-chain alkyl or polyol is used as a UV-curable component, and these ratios in the component are adjusted. You only need to raise it. Examples of long chain molecules include caprolactone-modified 2-hydroxyethyl acrylate, polyethylene glycol diacrylate (PEG), isodecyl acrylate, isooctyl acrylate, and the like. Also, for example, by using an ultraviolet curable component mainly composed of a urethane acrylate oligomer having a polyol structure, the Young's modulus at room temperature can be reduced. As the photopolymerization initiator, a normal photopolymerization initiator that generates radicals by irradiation with ultraviolet light, an electron beam, or the like may be used.
Benzoin ethers such as benzoin isopropyl ether and benzoin isobutyl ether; benzophenones such as benzophenone, p-methoxybenzophenone and p-bromobenzophenone; acetophenones such as benzyl methyl ketal, 2,2-diethoxyacetophenone and 1,1-dichloroacetophenone Thioxanthones such as 2-chlorothioxanthone, quinones such as anthraquinone and phenanthraquinone, and sulfides such as benzyl disulfide and tetramethylthiuram monosulfide.

As the pressure-sensitive adhesive, those obtained by adding a tackifier, a softener, a filler, an antioxidant, a cross-linking agent, and the like to the above-mentioned base polymer such as an acrylic polymer can be preferably used.

It is preferable that the above-mentioned hot melt type adhesive and pressure-sensitive adhesive contain a tackifier. As the tackifier, one or more of rosin resin, coumarone resin, hydrogenated petroleum resin, hydrogenated terpene resin, phenol resin and the like are preferable. Hydrogenated tackifiers have good compatibility, do not adversely affect thermal stability, and have a low water absorption, so they have little effect on corrosion resistance. Further, it is preferable that a softener is further contained as necessary. As the softener, one or more of process oil, paraffin oil, polybutene, polyisobutylene and the like are preferable. Note that additives such as a plasticizer, a wax, an ultraviolet absorber, a filler, and an antioxidant may be added as necessary.

Examples of the room-temperature-curable adhesive include a silicone rubber-based adhesive, a two-component adhesive, and a contact-curable adhesive. The silicone rubber-based adhesive is preferred in the present invention.

By appropriately selecting and combining the various components described above, the physical properties of the adhesive layer can be adjusted to the above-mentioned ranges.

The adhesive may be applied using a roll coater or the like. The adhesive may be applied to only one of the pair of substrates, or may be applied to both. After application, curing is performed if necessary. Alternatively, a configuration may be adopted in which a sheet of the adhesive is attached to a substrate, and then the substrates are attached to each other.

The thickness of the adhesive layer is preferably 10 to 100 μm, particularly preferably 40 to 80 μm. If the adhesive layer is too thin, the adhesive strength tends to be insufficient, and if the adhesive layer is too thick, the durability tends to be insufficient.

<Structure of Optical Disk> FIG. 1 shows an example of an optical recording disk as an example of the structure of the optical disk of the present invention. The optical recording disk shown in FIG. 1 has a pair of disk halves 10 bonded together with an adhesive layer 20.
The disk half 10 is provided with a film laminate 12 including at least a recording film and a protective film 13 covering the film laminate 12 on the surface of a resin substrate 11. The body 12 is adhered so as to be enclosed.

The resin substrate is transparent to recording light and reproduction light. When the thickness of the resin substrate is t and the diameter is φ, φ / t of each resin substrate is 180 or more, particularly 200
When the above is true, that is, when the ratio of the diameter to the thickness is large, the present invention exhibits a particularly high effect. The shape of the resin substrate is a disk shape, and its thickness is usually about 0.4 to 1.2 mm. Normally, both resin substrates have the same thickness. The constituent material of the resin substrate is not particularly limited, and may be appropriately selected from various resins such as acrylic resin, polycarbonate, epoxy resin, polymethylpentene, and polyolefin.

The type of the recording film is not particularly limited.
Phase change type recording films such as TeSb-based and TeGeSb-based, Tb
Any of a FeCo-based, GdFeCo-based magneto-optical recording film, a recording film containing an organic dye, and the like may be used. On both sides of the phase change type recording film or the magneto-optical recording film, at least one kind of various dielectrics such as silicon oxide, silicon nitride, zinc sulfide and the like is included in order to improve C / N and improve the corrosion resistance of the recording film. A dielectric film is usually provided. Between the dielectric film and the protective film, a reflective film made of Al, Au, Ag, or the like, or an alloy containing them is usually provided. Illustrated film stack 12
Is composed of a recording film, a dielectric film, a reflection film and the like.

The protective film is provided for improving corrosion resistance and abrasion resistance, and is preferably composed of various organic substances. In particular, a protective film containing a composition containing an ultraviolet curable compound is cured. It is preferable to be composed of a substance that has been subjected to the treatment.

When the present invention is applied to a read-only optical disk, similarly to a CD or the like, a resin substrate is provided with an information carrying portion such as a pit, usually a reflective film is provided thereon, and a resin film is further provided thereon. Is provided.

Although the illustrated example is a double-sided recording type optical recording disk, the present invention can be applied to a single-sided optical disk having an information carrying portion provided only on one resin substrate. In the case of the single-sided type, the same effect as in the case of the double-sided type can be obtained. It is preferable that the resin substrate (protective substrate) not provided with the information carrying unit is made of a resin having the same composition as the resin substrate provided with the information carrying unit, and has the same thickness.

When an ultraviolet-curable adhesive is used for the adhesive layer, it is necessary to irradiate ultraviolet rays or an electron beam after bonding a pair of disk halves. For this reason, the thicknesses of the recording film and the reflective film are appropriately set so that the required amount of ultraviolet rays and electron beams irradiated from the resin substrate side can reach the adhesive layer. In this case, it is only necessary that at least one half of the disk is capable of transmitting ultraviolet rays or electron beams. For example, the above-described protective substrate may be made of a material opaque to ultraviolet rays or electron beams.

The optical disk of the present invention usually has a size of 200 to 4
It is driven at a rotational speed of about 000 rpm.

[0036]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to specific examples of the present invention.

Sample No. 101 (Hot melt type bonding)
Agent) A 100 nm thick Al reflection film was formed on a polycarbonate substrate having a diameter of 120 mm and a thickness of 0.6 mm by a sputtering method. The ratio of the diameter φ to the thickness t of the substrate φ / t
Is shown in Table 1. The substrate was manufactured by injection molding, and at the same time, pits were formed on the surface. Next, a 20 μm-thick protective film made of an ultraviolet curable resin was formed on the reflective film to obtain a disk half.

Next, two disk halves each having a hot-melt type adhesive melt-coated on the surface of the protective film were bonded to obtain optical disk samples. The hot melt adhesive is a polystyrene-ethylene butylene copolymer block-like thermoplastic elastomer, a hydrogenated polybutadiene oligomer containing both terminal acryloyl groups (urethane acrylate type), polyisobutylene, a hydrogenated styrene-based tackifier, and a photopolymerization initiator. (Benzyl methyl ketal) was used. The thickness of the adhesive layer was 50 μm.

Sample No. 102 (Cold-Curable Adhesive) Produced in the same manner as Sample No. 101 except that a silicone rubber-based cold-cure adhesive {RTV silicone rubber (TSE392) manufactured by Toshiba Silicone Co., Ltd.} was used. .

Sample No. 103 (Adhesive sheet) Sample No. 10 except that the adhesive layer was composed of an adhesive sheet.
It was produced in the same manner as in Example 1. This pressure-sensitive adhesive sheet is a pressure-sensitive adhesive containing an acrylic base polymer and additives (tackifying resin, softening agent, filler, antioxidant, cross-linking agent, etc.), like a general pressure-sensitive adhesive. A material having an increased degree of polymerization and improved heat resistance was used. The pressure-sensitive adhesive sheet was attached to only one substrate.

Sample No. 104 (ultraviolet curing type bonding)
Agent) A sample was prepared in the same manner as in Sample No. 101, except that a UV-curable adhesive containing urethane acrylate as a main component and an additive such as a photopolymerization initiator was used and was cured by ultraviolet rays.

Sample No. 105 (Hot melt type bonding)
Agents) A lower dielectric film, a recording film, an upper dielectric film, a reflective film, and a protective film were formed on a polycarbonate substrate having the same dimensions as that of Sample No. 101, to produce a disk half. The substrate was manufactured by injection molding, and at the same time, a groove was formed on the surface. The recording film was of a phase change type made of an InAgTeSb-based alloy. Next, the two disk halves were adhered with an adhesive so that the recording film was enclosed therein, thereby obtaining an optical disk sample. The adhesive was sample No. 101
The same one was used.

Sample No. 201 (Hot melt type bonding)
Agent) AK- manufactured by Kanebo NSC as hot melt type adhesive
Except that Sample No. 1 was used, it was produced in the same manner as in Sample No. 101.

Sample No. 202 (Hot melt type bonding)
Agent) A sample was prepared in the same manner as in Sample No. 101, except that XW-13 manufactured by Toa Gosei Co., Ltd. was used as the hot melt adhesive.

Sample No. 203 (ultraviolet curing type bonding)
Agent) A sample was prepared in the same manner as in Sample No. 101 except that an ultraviolet-curable adhesive containing acrylic acid acrylate as a main component and additives such as a photopolymerization initiator was used.

Sample No. 204 (Hot melt type bonding)
Agent) polystyrene-polyisoprene copolymer (molecular weight 10
) Was prepared in the same manner as in Sample No. 101 except that a hot-melt adhesive consisting of

Sample No. 205 (Hot melt type adhesion)
Agent) Sample No. 20 except that the thickness of both substrates was 1.2 mm
In the same manner as in No. 4, it was produced. Table 1 shows φ / t of this substrate.

Table 1 shows the Young's modulus at 20 ° C. and the mechanical loss factor tan δ of the adhesive layer of each sample. The Young's modulus and tan δ were measured as follows. The adhesive was applied on a release paper in a layer having a thickness of 300 μm using a roll coater, and the ultraviolet-curable resin was cured by irradiating ultraviolet rays under the same conditions as in the preparation of the sample. The obtained adhesive layer was peeled off from the release paper, and measured at an excitation frequency (sine wave) of 10 Hz using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho. With respect to the pressure-sensitive adhesive, a measurement sheet having a thickness of 300 μm was prepared and measured in the same manner.

The following tests were performed on each sample.

The vibration resistance test sample was set on a spindle motor, and the sample was applied at 1800 rpm while applying vibrations assuming that the vehicle was running.
And the displacement of the outer peripheral portion of the sample accompanying the rotation (displacement in a direction parallel to the rotation axis) was measured. The sample displacement was determined from the servo displacement of the lens of the optical pickup. The measuring position is the outermost track (distance from center 5
8 mm). The vibration was continuously changed in 5 minutes from a low-frequency large amplitude of 10 Hz × 1 mm to a high-frequency small amplitude of 100 Hz × 100 μm. Table 1 shows the results
Shown in For comparison, Table 1 shows the displacement when rotated without applying vibration as an initial value.

Heat resistance test The sample was heated to 1800 in an atmosphere of 60 ° C. and 30% RH.
After rotating at rpm for 300 hours, the average warpage angle of the sample was measured. Table 1 shows the results. For comparison, the average warp angle of the sample before the heat resistance test is shown in Table 1 as an initial value.

[0052]

[Table 1]

From the results shown in Table 1, the effect of the present invention is clear. In Sample Nos. 101 to 105 in which the Young's modulus and tan δ of the adhesive layer were within the range of the present invention, the displacement during rotation was slightly increased in the vibration resistance test, but was sufficiently within the practical allowable range where there was no problem in recording and reproduction. It is considered that the adhesive layer absorbed the external vibration and suppressed the displacement. In addition, in these samples, even if the sample is rotated for a long time in a high-temperature environment, the increase in the warp angle is small, and it can be seen that the deterioration in the mechanical accuracy of the sample is small.

On the other hand, the Young's modulus and tan
Sample No. where at least one of δ is out of the range of the present invention.
In Nos. 201 to 204, the vibration resistance or heat resistance is not practical. However, in Sample No. 205, there is no problem in heat resistance and vibration resistance because a substrate having a small φ / t is used. From these results, it is understood that the present invention is effective for a substrate having a large φ / t.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration example of an optical disc of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Disc half 11 Resin substrate 12 Film laminated body 13 Protective film 20 Adhesive layer

Claims (5)

[Claims] An information carrying portion is provided on at least one of the resin substrates, and the pair of resin substrates are bonded by an adhesive layer such that the information carrying portion is enclosed. When the thickness of the resin substrate is t and its diameter is φ, φ / t of each resin substrate is 180 or more, and the Young's modulus of the adhesive layer at 20 ° C. is 0.1 kgf / mm ²
An optical disc having an ultra-low 1 kgf / mm ² or less and a mechanical loss coefficient tan δ at 20 ° C. of 0.6 to 5.0. 2. The optical disk according to claim 1, wherein said adhesive layer is made of a hot melt type adhesive. 3. The optical disk according to claim 1, wherein said adhesive layer is made of an adhesive. 4. The optical disc according to claim 1, wherein said adhesive layer is made of a cold-setting adhesive. 5. The optical disk according to claim 1, wherein said adhesive layer is made of an ultraviolet curable adhesive.